Study On The Influencing Factors And The Physicochemical Properties Of Resistant Starch For Chinese Yam(Dioscorea Opposite Thunb.)Tuber

Resistant starch (RS) is a new starch discovered in recent years. It is the general term of starch and decomposition products which are not digested and absorbed by small intestine of healthy. Plant resistant starch is similar to dietary and is one kind of polysaccharide which has special physiological functions. It was reported there were nutritional values and medicinal functions in plant resistant starch. Many scientists were interested in it and did some research work on different plant resistant starch.The influencing factors and the physicochemical properties of resistant starch of Chinese Yam (Dioscorea opposite Thunb.) tuber was investigated in this study. Contents of resistant starch and the main components in Chinese Yam tuber were detected and the correlation between main components and starch and the correlation between main components and resistant starch was analysis respectively. The influence factors about the formation of resistant starch in Chinese Yam tuber were explored. The physical and chemical properties resistant starch of Yam was investigated and analyses based on Scanning Electron Microscope, X-ray Diffractometer, Differential Scanning Calorimetry (DSC) Analyzer and Ultraviolet Spectrophotometer and other precise instruments. The main results were as follows:1. The alkali extraction was the optimal method for Yam starch extraction without lot of mucous protein in tuber and with high purity of starch and low cost and low environment pollution. The purity of starch could be up to more than97%if this method was applied repeat.2. The correlation was analysis between the main components and starch and the main components and resistant starch respectively. The main components of Chinese Yam played a certain effect on formation both starch and resistant starch. There was a significantly positive correlation between starch content and dry matter content(R=0.732**) of Yam.It was a significant negative correlation between starch content and soluble starch content(R=-0.781**). It was a significant positive correlation between resistant starch content and amylose content(R=0.492*). It was a significant positive correlation between RS and the ratio of amylose/amylopectinCR=0.485*).It was a negative correlation (R=0.522*) between RS and soluble sugar content.3. It is clear that concentration of starch milk, pH, autoclaving temperature and autoclaving time was the main factors of influencing the yield of resistant starch by detected the single influence factors on RS production with different autoclaving temperature, autoclaving time, concentration of starch milk and pH. The optimum parameters for RS of Yam were15%starch milk concentration,5.5pH value,125℃autoclaving temperature,2.5h autoclaving treatment time by43orthogonal test.28.49%RS production was obtained from Yam tuber. The order of functional factors was autoclaving temperature stronger than autoclaving time than the starch milk concentration and than pH value.4. The results of physicochemical properties of yam resistant starch showed that RS morphology was not smooth with irregular shapes compared with starch. B-type map of starch of Yam was the mainly type showed by X-ray. There was a different crystal structure of RS compared with starch and some of crystal structure was damaged during hot-press treatment. However, it was still a B-type map. There was a clear melting endothermic peak of Yam RS under Differential Scanning Calorimetry (DSC) analysis. The highest peak was on72.9℃-103.1℃.5、The acid resistance and water absorption tests showed that yam resistant starch had higher acid tolerance and water absorption than yam starch. Enzyme digestion test showed that it was stronger of yam RS than potato resistant starch and it was more difficult on enzyme digestion also.The iodine absorption curve result of the yam RS showed that the maximum wavelength of resistant starch-iodine absorption curve was shorter than the maximum wavelength of amylose-iodine absorption curve.